Figure 2.

(a) Reconstruction of the caudal region in Sacabambaspis janvieri, assuming a moderately hypocercal condition, and the presence of a small ventral web. Same abbreviations as for figure 1. (b) Distribution of the hypo- and epicercal conditions of the tail in one of the current phylogenies of the major living and fossil vertebrate taxa. The position of the notochord (grey) is entirely hypothetical in the anaspids, heterostracans, osteostracans and the thelodonts Furcacauda and Loganellia. (Acrania as sister group to vertebrates; tree topology after Sansom et al. 2005.) See text for the characters at nodes (after Wilson & Caldwell 1993; Janvier 1996; Donoghue et al. 2000; Zhang & Hou 2004).